>    Can anybody show me the best way to read a 4-20mA sensor?


>    Any url link or help will be very appreciated.




Hi Eduardo,


Try the TI INA117. Here is a link to the datasheet 




Look at page 8 diagram (a). The internal precision resistor

network gives this chip a common mode voltage range of +/- 200v,

so it doesn't matter where it goes in the current loop.


The only downside to the INA117 is that you will need at least

+/- 10v supply. I usually use an ICL7660 or a MAX232 to 

generate a low current negative supply for apps like this.


TI will send you overnight samples of the INA117 and MAX232

at no charge.


I have attached a gif of an input protection circuit for the

PIC A/D to limit the input voltage to approx. Vcc +.3/gnd -.3

in case your loop uses a 120% signal to indicate sensor burnout.

For diodes the 1N5817 would be a good one, or if you can deal 

with surface mount, the Central Semi CMPSH-3S are great.

That is a surface mount package with 2 diodes series connected.

If you would like a few of those, just send me your address

off list, and I will mail you a few.


An input protection circuit like this ia a good idea ANY time

that a PIC input connects to the outside world.


Good luck,